Circuit board fabrication has become an increasingly complex and expensive process as circuit boards become more densely packed with electrically communicating components. Various chemical layering techniques have been developed for isolating electrically conducting lines or traces on circuit boards. For lines or traces that could electrically interfere with one another by, for example, undesirably intersecting, these traces are separated or dispersed onto different layers and are insulated from each other. Thus, there may be a substantial number of layers of traces that make up the entire printed circuit board, depending on the geometry of the traces and the placement of components on the printed circuit board. A significant number of conducting traces are also electrically connected to pads to which electrical components are connected, such as integrated circuit chips.
Additionally, since such traces must also ultimately connect with either the electrical components provided on the circuit board pads or other traces on other layers, a large number of holes, i.e., via holes and blind holes (as they are known in the art), are typically provided as part of the circuit board for electrically communicating between the layers of the circuit traces. In fact, there may be as many as 30,000 to 40,000 such holes provided on a single circuit board.
Circuit board fabrication using such a trace layering strategy suffers from a number of drawbacks, including:
(1.1) The chemical interactions and steps required during circuit board fabrication may be relatively large, i.e., 30 to 120 different steps; PA1 (1.2) The large number of holes increases the circuit board fabrication cost; PA1 (1.3) A circuit board that is found to be defective is typically not repairable since circuit traces are embedded with the circuit board substrate; PA1 (1.4) Many of the chemicals used in circuit board fabrication require special handling for disposal; PA1 (1.5) The fabricated circuit boards have relatively low tolerances to heat; i.e., they may be unreliable above 135.degree. F.; PA1 (1.6) It is not easy to provide other than planar circuit boards, for example, fabricating circuit boards in the form of cylinders is difficult; PA1 (1.7) It is not possible to provide circuit boards with a substrate such as, for example, aluminum; and PA1 (1.8) The length of individual traces may be longer than desired thereby slowing the processing efficiency of the circuit board.
Thus, it would be advantageous to provide a circuit board fabrication process that alleviated or at least mitigated the above drawbacks.